A cataract is a loss of normal transparency of the lens. Any opaque spot on the lens, regardless of its size, is technically a cataract. A cataract that is visible to the naked eye appears as a milky gray film behind the pupil.
The majority of cataracts in dogs are genetically determined, but the mode of inheritance varies among breeds. Congenital cataracts (also called juvenile cataracts) have been described in more than 75 breeds, including Cocker Spaniels, Bichons Frises, Boston Terriers, Wire Fox Terriers, West Highland White Terriers, Miniature Schnauzers, Standard Poodles, Siberian Huskies, Golden Retrievers, Old English Sheepdogs, and Labrador Retrievers.
Juvenile cataracts appear in dogs before they are 6 years of age and usually involve both eyes, although not necessarily at the same time. A genetic test for some of the affected breeds is under development through VetGen.
Acquired cataracts occur as a consequence of aging and other eye diseases, most notably uveitis. Dogs with diabetes can develop cataracts in a matter of weeks. Puppies fed milkreplacement formula that is deficient in arginine can develop bilateral cataracts. Newer formulas have been adjusted for this problem.
Senile cataracts are a major cause of blindness in dogs 6 to 8 years of age and older. These cataracts begin at the center of the lens and gradually spread out toward the periphery like the spokes of a wheel.
When the lens becomes uniformly opaque, the cataract has reached its mature stage. Senile cataracts often occur in both eyes, but seldom develop at the same rate. One cataract generally matures before the other.
Senile cataracts should be distinguished from nuclear sclerosis, a normal aging of the lens in which new fibers are continually forming at the periphery of the lens and pushing inward toward the center. These changes cause a bluish haze in the lenses of older dogs. This haze does not interfere with vision.
Treatment: Senile cataracts do not need to be treated unless both eyes are involved and the degree of blindness is such that the dog is having difficulty getting around. Visual impairment can be corrected by surgery - removing the lens, either by extraction or preferably by an operation called phacoemulsification, which first breaks down the lens.
Without a lens, the image the dog sees is blurred and the edges are indistinct, but objects can be seen. Replacement with an artificial lens (intraocular lens replacement) is an option.
Some juvenile cataracts will be spontaneously reabsorbed, usually within one year of their appearance. Complete resorption results in vision comparable to that of successful lens surgery. If the cataract is breaking down on its own, as in resorption, surgery should not be done.
Prevention: Hereditary cataracts can be prevented by not breeding affected dogs and those who carry the gene. Dogs with congenital cataracts can be identified by annual eye examinations carried out by veterinary ophthalmologists affiliated with the Canine Eye Registry Foundation.
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